binary_search_by_key comparator returns reference

Author: circuitfox

src/libcollections/slice.rs

@@ -1125,8 +1125,8 @@ impl<T> [T] {
     #[stable(feature = "slice_binary_search_by_key", since = "1.10.0")]
     #[inline]
     pub fn binary_search_by_key<'a, B, F, Q: ?Sized>(&'a self, b: &Q, f: F) -> Result<usize, usize>
-        where F: FnMut(&'a T) -> B,
-              B: Borrow<Q>,
+        where F: FnMut(&'a T) -> &'a B,
+              B: Borrow<Q> + 'a,
               Q: Ord
     {
         core_slice::SliceExt::binary_search_by_key(self, b, f)

src/libcore/slice/mod.rs

@@ -131,8 +131,8 @@ pub trait SliceExt {
 
     #[stable(feature = "slice_binary_search_by_key", since = "1.10.0")]
     fn binary_search_by_key<'a, B, F, Q: ?Sized>(&'a self, b: &Q, f: F) -> Result<usize, usize>
-        where F: FnMut(&'a Self::Item) -> B,
-              B: Borrow<Q>,
+        where F: FnMut(&'a Self::Item) -> &'a B,
+              B: Borrow<Q> + 'a,
               Q: Ord;
 
     #[stable(feature = "core", since = "1.6.0")]
@@ -612,8 +612,8 @@ impl<T> SliceExt for [T] {
 
     #[inline]
     fn binary_search_by_key<'a, B, F, Q: ?Sized>(&'a self, b: &Q, mut f: F) -> Result<usize, usize>
-        where F: FnMut(&'a Self::Item) -> B,
-              B: Borrow<Q>,
+        where F: FnMut(&'a Self::Item) -> &'a B,
+              B: Borrow<Q> + 'a,
               Q: Ord
     {
         self.binary_search_by(|k| f(k).borrow().cmp(b))

src/test/run-pass/slice_binary_search.rs

@@ -24,6 +24,6 @@ fn main() {
     ];
 
     let key: &str = "def";
-    let r = xs.binary_search_by_key(&key, |e| &e.topic);
+    let r = xs.binary_search_by_key(key, |e| &e.topic);
     assert_eq!(Ok(1), r.map(|i| i));
 }